The present invention relates to a pressure sensing device for use in pipelines transporting slurries, corrosive or abrasive fluids wherein it is essential to isolate the pressure gauge from the fluid being transported. A thin metal wall forming a portion of a removable sleeve serves as a means to transmit pressure signals from the fluid medium being transported within the pipeline to a liquid filled pressure sensing chamber operatively connected to a pressure gauge. The thin metal wall is provided with means to permit the wall to move inwardly and outwardly in response to small pressure changes.
There are numerous pressure gauges in the prior art which are particularly adapted to isolate the pressure media from the sensor. These devices provide for a diaphragm or membrane which forms a barrier between the media passing through the pipeline and a fluid filled chamber on the opposite side of the diaphragm with the fluid filled chamber being operatively connected to a pressure gauge. Thus, the diaphragm or membrane responds to pressure fluctuations within the fluid passing through the pipeline and transmits pressure signals to the fluid within the isolating chamber which in turn actuates the pressure gauge. Examples of such devices are the Classen U.S. Pat. No. 4,425,800, Borsanyi U.S. Pat. No. 3,863,504, Knecht U.S. Pat. No. 4,773,269 and Mayhew U.S. Pat. No. 4,840,068.
The Classen U.S. Pat. No. 4,425,800 discloses a device for determining the internal pressure in a fuel injection pipe system wherein a housing member has a wall portion of reduced thickness so as to act as a membrane and which transmits the pressure signals from the pipe system to a sensor device. The Borsanyi U.S. Pat. No. 3,863,504 discloses a pressure gauge wherein the instrument is separated from the pipeline by a flexible diaphragm. The Knecht U.S. Pat. No. 4,773,269 also provides a deflecting diaphragm member which senses a pressure within a chamber and by deflection of the diaphragm a change of resistance takes place in a strain gauge mounted on the diaphragm. The Mayhew U.S. Pat. No. 4,840,068 provides a pipe pressure sensor in which an elastomeric member is utilized as a flexible diaphragm disposed between a pipeline and a pressure sensing liquid chamber.
There are, however, problems in connection with the use of such prior art devices. Flexible elastomer diaphragms tend to absorb liquids and are damaged by corrosive media and slurry particles passing through the pipeline. Accordingly, the response of such diaphragms vary considerably depending upon the condition of the elastomer. Pressure sensors which utilize relatively thin metal walls as a means for separating the pipeline media from contact with the pressure gauge do not respond well to small pressure changes due to a lack of flexibility and, of course, such elements are subject to deterioration by corrosion and the like. Furthermore, not one of the prior art devices provides means for measuring pipe pressure around the entire circumference of the fluid stream. It can be appreciated that in large pipelines carrying heavy slurries the weight of the slurry itself will have an appreciable effect on pressure measurements and hence it is essential to provide a means for measuring the pressures around the entire fluid stream.
According to the present invention, there is provided a pressure sensing device which includes a readily replaceable sleeve having a thin walled metal member which serves as a pressure sensing diaphragm extending around the entire circumference of the fluid stream. The metal pressure sensing diaphragm is provided with means comprising pressed out accordion-like pleats or folds to permit movement of the diaphragm in response to small pressure changes so as to provide a highly accurate pipe pressure measuring device. Thus, the present invention overcomes the above-noted disadvantages of prior art pipeline pressure gauges by utilizing a thin walled metal diaphragm having accordion-like folds therein extending 360.degree. around the periphery of a fluid stream to permit instantaneous response to small variations in pressure within the pipeline. The sensing diaphragm is mounted on a sleeve which is screw-fit within the body member with the pressure gauge mounted externally of the body member. Thus, the sleeve may be readily replaced in the event the diaphragm becomes damaged.
An object of the present invention is to provide a pipeline pressure sensor which utilizes a metallic diaphragm including accordion-like folds to ensure accuracy of pressure measurements.
Another object of the present invention is to provide a pressure sensing device for pipelines in which the pressure sensing diaphragm extends around the entire periphery of the fluid stream.
Other objects and many of the intended advantages will become more readily apparent upon consideration of the following detailed specification when considered in connection with the accompanying drawings wherein: